1. Field of the Invention
This disclosure is related to video processing, and more particularly, to motion estimation and compensation for a periodic pattern.
2. Description of the Related Technology
In video processing, typically only a fraction of an image changes in an image frame sequence, allowing prediction of object movement in the frame sequence. Motion compensation is used as part of the predictive process. If a frame sequence shows moving objects, then the objects' motion within the scene can be measured, and this information may be used to predict the content of frames later in the sequence of frames or between frames.
In video encoding, motion estimation is used to eliminate the temporal redundancy of video information and therefore forms a central part of video coding standards. As such, motion compensation relies on motion estimation for many video processing applications. Motion compensation is used in video compression (such as MPEG-2 and MPEG-4), frame rate conversion, noise reduction, de-interlacing, and format conversion. The core function of motion compensation and motion estimation is to find motion between sequential video frames or, equivalently, to find motion vectors between objects in the frames.
Many motion estimation methods have been developed. The simplest motion estimation method is a block-matching algorithm, wherein the pixel values in blocks of each frame are estimated by a displaced block of similar shape and size in a past frame. As such, this method finds the best match for a block of a target picture frame within a search area in a reference picture frame. Estimating motion results in a motion vector, which represents the geometrical displacement between the two matched blocks. The motion vector is determined by finding a vector that essentially minimizes a cost function that is a measure of mismatch between the reference and the target blocks. Other, more advanced motion estimation algorithms may also be employed.
A disadvantage of conventional motion estimation methods is that in some cases the determined motion vector is incorrect. Incorrect estimation of a motion vector may introduce visual artifacts in a motion-compensation interpolated image.